1. Field of the Invention
The present invention relates to an illuminating device.
2. Description of Related Art
Conventionally, an incandescent lamp or a fluorescent lamp is generally used as a light source for general lighting such as room lighting. In recent years, due to increase in performance of a blue light-emitting diode (LED), such a light emitting diode has been used as a light source of a ceiling lamp, downlighting and the like (see Japanese Patent Application Laid-Open No. 2007-220465).
FIG. 14 illustrates a so-called pseudo white LED 100 that can be used as a light source of an illuminating device. The pseudo white LED 100 has a lamp house 104 and transparent resin 106. A plurality of blue light-emitting diodes 102 as light emitting devices is arranged adjacent to each other on a bottom portion of the lamp house 104. A concave portion of the lamp house 104 is sealed by the transparent resin 106. Moreover, yellow phosphor 108 such as garnet (YAG) is dispersed in the transparent resin 106. Blue light emitted by the respective blue light-emitting diodes 102 is diffused in the transparent resin 106 of the lamp house 104, where a wavelength of the blue light is converted by the yellow phosphor 108 into fluorescent yellow light. Then, the light is output as outgoing light L (L1, L2) as represented by a chain double-dashed line for the sake of convenience, to the outside of the lamp house 104. In addition, a reference numeral 103 in FIG. 14 denotes an electrode terminal.
Moreover, as illustrated in FIG. 15, a lens sheet 110 is arranged in front of the pseudo white LED 100. The outgoing light L from the pseudo white LED 100 is deflected by the lens sheet 110 to a desired direction, which enables a function as the illuminating device. The lens sheet 110 shown in FIG. 15 has a first lens group 112 and a second lens group 114. As seen from an optical axis C of the pseudo white LED 100 as a center, the second lens group 114 is arranged on an outer side of the first lens group 112, and the first lens group 112 is arranged on an inner side of the second lens group 114. The first lens group 112 has a refraction prism. The second lens group 114 has a reflection (TIR: Total Internal Reflection) prism lens.
An output angle of the outgoing light L from the pseudo white LED 100 is deflected by both the first lens group 112 and the second lens group 114 to a direction parallel to the optical axis C.
Regarding the light emitting by the illuminating device using the pseudo white LED 100 as the light source as described above, there is the following tendency; that is, when the optical axis C of the pseudo white LED 100 is considered as a center, a central portion is slightly tinged with blue and an outer portion is slightly tinged with yellow. The reason is as follows. In FIG. 14, the outgoing light L1 follows a light path that is parallel to the optical axis C of the pseudo white LED 100, while the outgoing light L2 follows a light path that is inclined with respect to the optical axis C of the pseudo white LED 100. Therefore, the outgoing light L2 passes through the transparent resin 106 in which the yellow phosphor 108 is dispersed for a longer light path length and thus a rate of the wavelength conversion to fluorescent yellow light due to the yellow phosphor 108 becomes higher, as compared with the outgoing light L1.
In addition, in the above illuminating device, the pseudo white LED 100 having the plurality of blue light-emitting diodes 102 arranged adjacent to each other is used as the light source. In this case, the light emitting by the illuminating device may cause color unevenness called “chip appearance” on an irradiated area. This is a visible phenomenon caused by a series of light with high chromaticity and high brightness among the outgoing light from the respective blue light-emitting diodes 102 on the irradiated area.
Such the color unevenness of the illumination light causes deterioration of quality. This is not a matter in a case of a conventional illuminating device using an incandescent lamp or a fluorescent lamp but peculiar to the illuminating device using the pseudo white LED 100 as the light source.